Low-temperature chamber refrigeration



Aug. 13,1946. 7 onw e 2,405,895

LOW TEMPERATURE CHAMBER REFRIGERATION Filed May 28 1.942

INVENTOR ATTORNEYS Patented Aug. 13, 1946 LOW TEMPERATURE CHAMBERREFRIGERATION Erwin Lodwig, Franklin Square, N. Mobile Refrigeration,Inc., New

corporation of New York Y., assignor to York, N. Y., a

Application May 28, 1942, Serial No. 444,800

6 Claims.

This invention relates to refrigeration and more particularly concernsimproved apparatus for rapidly cooling the atmosphere in a chamber tovery low temperatures.

In the development and testing of aircraft, parts thereof, andinstruments and other apparatus for use thereon, it is necessary tosubject various parts and devices to the extreme conditions ofatmospheric'temperature and pressure encountered in flight. Theseconditions include temperature changes from the highest groundtemperature to temperatures well below 100 degrees below zeroFahrenheit, and pressure changes from normal atmospheric pressure at sealevel to less than four inches of mercury absolute. Since the conditionsto be reproduced include subatmospheric pressures, a closed chamber mustbe used, and in order that the operation of the instruments or devicesmay be observed, a window or sight opening is preferably provided in thechamber.

In the operation of a chamber under the conditions described, theformation of frost is a serious problem. Moisture is condensed from theair within the chamber as its temperature is lowered below the dew pointof the air, and freezes on the evaporators or other surfaces employed tocool the chamber. Further, it is frequently necessary to open thechamber while the atmosphere therein and the interior surfaces thereofare at very low temperatures, and under such conditions, frost quicklyaccumulates on the cold interior surfaces of the chamber, including theinner surfaces of any windows or sight openings therein. This frostingis caused by the entry of air at room temperature and relative humidityand the sudden condensation and freezing of moisture from such air whenits temperature is lowered, by mixture with the cold air and contactwith the cold surfaces within the chamber. The frost both obscuresthesight opening and reduces the efficiency of the cooling surfaces bypartially insulating them from the air within the chamber so that therate of coolin of the chamber air is retarded and it is impossible toaccurately observe the operation of devices in the chamber through thewindow.

With the above and other. considerations in mind, it is proposed inaccordance with the present invention to devise an improved chamberhavin cooling means capable of rapidly lowering the temperature of theair in the chamber to very low values without producing frostaccumulations thateither obscure a window in the chamber orsubstantially retard the rate of cooling of the chamber air. I havefound it desirable in chambers of the type described to provide separaterefrigerant evaporating means for respectively cooling the walls of thechamber and the air in the chamber. I have further discovered that bycirculating the air in the chamber successively over the separateevaporating means but at a higher velocity over the air coolingevaporator than over the wall cooling evaporator means, accumulations offrost or ice may be removed from the air cooling evaporator, and theaccumulation of frost on that evaporator when the chamber is closed maybe avoided. I have also discovered that accumulations of frost may bequickly removed from the inner surface of a sight opening or window inthe chamber by successive circulation of air in the chamber over thewindow and the cooled chamber walls.

Other objects, advantages, and features of the invention will beapparent from the following description of a typical embodiment thereofwhich is illustrated in the accompanying drawing.

In the drawing Fig. l is a sectional elevation illustrating arefrigerating chamber provided with cooling means and. embodying myinvention;

Fig. 2 is a sectional view of the air cooling evaporator taken along theline 2-2 of Fig. l and viewed in. the direction of the arrows; and

Fig. 3 is a sectional view on a reduced scale of one of the wallevaporators of the chamber illustrated in Fig. l.

Refrigerated chambers embodying the invention may be of any desired formand are usually rectangular or cylindrical. The chamber illustrated inthe drawing is rectangular and its six surfaces comprise a door D andfive wall sections, of which four are illustrated in Fig. l at W, W1,W2, and W3. Since the chamber is substantially completely evacuated inuse, itswalls must be strong enough to withstand substantially fullatmospheric pressure. This could be accomplished by constructing thewalls of heavy gauge metal, but I prefer instead to employ wall sectionsformed of two spaced metal plates or sheets having passagestherebetween. This arrangement provides walls having the requisitestrength and relatively little mass, whereby the heat load imposed bythe walls is reduced. The arrangement also provides passages between thewall plates so that the wall sections comprise evaporators in whichrefrigerant may be evaporated to cool the 1 Walls, and, to some extent,the air in the chamber.

In the illustrated embodiment, each wall section comprises two spacedmetal plates 4 and 5.

connected along their edges by edge spacers 6 and at intermediate pointsby reinforcing bafile spacers 7. The baffle spacers l are preferablystaggered as shown in Fig. 3 to provide a circuitous passage between thewall plates for the flow of refrigerant. The edge spacers S are welded"or otherwise tightly sealed to the wall plates 4 and 5 so that eachWall section forms a sealed refrigerant evaporator. The several wallsections W, W1, W2, etc., may be of identical construction and arewelded together alcngtheir meeting edges to form an air-tight chamber.Instead of using the spacers E and 7, the plates 4 and 5 may be offsetor embossed to provide meeting areas that define circuitous'refrigerantpassages between the plates. of the chamber walls may be heatinsulatedby any suitable material, and such insulation has beendiagrammatically represented at M.

The chamber door D may be of any suitable construction, and as showncovers substantially allot one'surface of the chamber. The door D may behingedly secured to a frame or flange 8. around the door opening, andmay be held closed by suitable clamps or latches,not shown. A sightopening or window .0 is preferably provided in the chamber door D, andas shown may comprise a plurality of spaced glass panes 9 and 10; sealedin theframe ll of the door. Spaced gaskets l2 and 13 may .be providedbetween the dolor frame H and the chamber opening flange 8 to insure atight closure. I

A-n evaporator E is provided within the charm berfor cooling the airtherein and the instruments or other apparatus under test orobservation; In accordance with the present invention, means areprovided for. circulating air in the chamber successively .over thisevaporator and theinner surfaces of the chamber wall section evaporatorsW, W1, W2, etc. The arrangement is such that the velocity of thecirculated air passing over the evaporator E .is considerably higherthan that of the air passing over the chamber wall surfaces. In thedisclosed. embodi- -ment,.the evaporator E comprises a coil I 5 having avertically disposed heat conductingfms I 6 thereon, andthefinnedcbil-unitiis enclosed in afiue or dust H. The flue H has a fancompartment l8 below the evaporator coil .|5.and in communicationtherewith through an opening [9. Anair inlet opening is provided in thefront wall of the flue l1, and an outlet opening 2| is provided in thefront wall of the fan compartment l8. l A fan or blower .22 of anysuitable construction is disposed. to propel air at relatively highvelocity through the flue l1, and as shownthis fan-is disposedajdjacentthe outlet opening 2| of the fan compartment [3. The fan22 may bedrivenby an electric motor. 23..

The assembly comprising theevaporator E and flue I! is preferably spacedfrom the window 0 and may be disposed as shown adjacent the back wallsection W1 of the chamber with the air inlet and outlet openings 20 and2| directed toward the "opposite wall of the chamber, in the illustratedembodiment toward the chamber door D;

The evaporator coil 15 and thewall section evaporators are supplied withrefrigerant from any suitable source such as a; refrigerant compressingand condensing unit, conventionally represented at 25. The coil 15 ofthe evaporator E may be supplied with condensed refrigerant throughapipe 26-, and evaporated refrigerant may be returned from the coil tothe unit The outer surfaces practice,

' In the operation of the illustrated embodiment of my invention,considering first the cooling of the chamber and the air and equipmenttherein from room temperature to a low temperature required for test ordevelopment operations, the door D is closed and the refrigeration unit25 and fan 22 are started. Due to the arrangement of the flue 11, theair propelled by the fan 22 is confined to a path closely adjacent thecoil 15 and fins l6 of the evaporator E and flows at a relatively highvelocity over these parts, whereas the air is circulated at lowervelocities over the inner surfaces of the chamber walls and the pane 9of the window 0. Refrigerant evaporates in the chamberwall sections W,W1, W2, etc., and rapidly withdraws heat therefrom, thereby reducing thechamber wall temperature. At the same time, the evaporator E rapidlycools the air in'the chamber, and the instruments and devices therein.As the cooling progresses, the temperature of the chamber walls fallsbelow the dew point of the air in the chamber and belowthe freezingpoint, with the result that moisture is condensed from the air andfrozen on the inner surfaces of the walls. The temperature of theevaporator E also falls below the dew point of the air and the freezingpoint of water, and the accumulation of frost on the evaporator coil l5and fins I 8 would also be expected. However, with the air flowing overthe evaporator E at a considerably higher velocity than over the charmber walls, frost does not form on the evaporator E. The temperature ofthe instruments or other apparatus under test or observation in thechamber also falls below the dew point and the freezing point as theseobjects are cooled by the circulated air, but frost does not accumulatethereon.

The selective formation of frost on the chamber walls rather than on theevaporator E is apparently caused by the more rapid circulation of airover the evaporator which transfers heat thereto more rapidly than tothe walls and accordingly maintains the evaporator at a somewhat highertemperature than the walls. Similarly the absence of frost on theapparatus under test in the chamber is believed due to the fact thatsuch apparatus, being cooled by the circulated air, is at a highertemperature than the chamber walls. Regardless of the reason for thisselective frost formation, the observed fact is that even after frosthas accumulated on the surfaces of the evaporator E and; on apparatus inthe chamber, due to the opening of the chamber door D when the surfacesandapparatus are below freezing temperature, operation of the fan 22with the door D closed rapidly removes not only the frost accumulated onthe evaporator and the apparatus, but that formed on the inner surfaceof the glass pane 9 of the window 0 as well.

It is frequently necessary to :open the chamher door D to give access toinstruments or devices in the chamber while the air in the chamber, the.apparatus therein, the evaporator E,

point. Before opening the door D, the fan 22 is stopped to avoidunnecessary heating by blowing chilled air out of the chamber. When the.door D is opened, relatively warm moist room air enters the chamber andmingles with the cold air therein. The moisture introduced by the roomair increases the relative humidity of the mixed air in the chamber to apoint above saturation at the prevailing mixed air temperature with theresult that immediate condensation takes place, forming a fog or mist inthe chamber. The temperature of the chamber walls, the evaporator E,.theinner surface of the glass pane 9 of the window and any apparatus undertest in the chamber, are not only well below the dew point of themixedair, but below the freezing point as well. Therefore, frost quicklyforms on these surfaces within the chamber. The formation of frost onthe pane 9 is particularly rapid, since with the door open, the coldpane is in direct contact with warm moist room air. The formation offrost on apparatus in the chamber prevents accurate observation thereof,particularly in the case of the dials or glass cover plates ofindicating instruments, and if permitted to remain, such frost mightimpair the operation or accuracy of certain devices. When the chamberdoor D is again closed and the fan 22 started, the frost quicklydisappears from the evaporator E and also from the inner surface of thewindow pane 9. At the same time, frost is quickly removed from thedevices in the chamber. Removal of frost from the pane 9 and from thedevices permits clear observation of the devices in the chamber.Defrosting of the evaporator coil E increases the rate at which heat isabsorbed thereby from the chamber air. As a consequence, the chamber airtemperature is quickly lowered to the desired value, the cooling of theinstruments or devices in the chamber is not delayed, and the testing ordevelopment work proceeds rapidly.

It is my belief that the above described defrosting of the evaporator E,the Window pane 9,

and apparatus in the chamber involves a transfer of frost from theseparts to the inner surfaces of the chamber wall evaporator sections W,W1, W2, etc., and results from the difference in temperature of theseveral parts and the successive circulation of air thereover. Since theair in the chamber is circulated at a higher velocity over theevaporator E than over the chamber wall evaporator surfaces, theevaporator E is maintained at a somewhat higher temperature than thechamber walls. The apparatus in the chamber which is cooled by thecirculated air, is at a higher temperature than the chamber walls. Also,heat loss through the window structure O keeps the inner window pane 9at a higher temperature than, the chamber wall evaporator surfaces. Itis therefore probable that the air circulating at relatively lowvelocity along the surfaces of the chamber wall evaporators is chilledto a temperature where moisture is condensed therefrom and deposited onthese walls in the form of frost, reducing the moisture content of theair at this point. The air thus dried or dehydrated then passes over thesurfaces of the evaporator E and the window pane 9, and over theapparatus under test in the chamber, its temperature is raised bycontact with these relatively warmer surfaces and its relative humidity,is thereby decreased, The air then apparently picksup moisture fromthese surfaces by sublimation of the frost. thereon. Although thisexplanation is believed correct, it should be understood that theinvention is in no way dependent upon the accuracy thereof.

I claim: 1

1. In apparatus of the type described, in combination, a closed chamberhaving a: window therein, at least two evaporators disposed at spacedpoints, in said chamber and having surfaces exposedto the atmospheretherein, means for supplying refrigerant to said evaporators wherebytheir exposed surfaces are cooled, and means including an air propellingdevice for circulating some of the air within said chamber successivelyover said evaporators and said window and at a higher velocity over oneof said evaporators than over the window and the other evap orator,whereby frost accumulations are removed from the window and from theevaporator over which the air is circulated at the higher velocity.

2. In apparatus of the type described, in combination, a closed chamberhaving at least a portion of its wall structure formed of metallicplates spaced to provide passages for the evaporation of refrigeranttherebetween, an evaporator in said chamber spaced from the chamber wallstructure, means for supplying refrigerant to said wall structurerefrigerant passages and to said evaporator whereby said evaporatorandthe inner surfaces of said portion of said wall structure are cooled,and means including an air propelling device for circulating air in saidchambersuccessively at high velocity over said evaporator and at arelatively lower velocity over the cooled inner surfaces of said portionof said wall structure, whereby accumulation of frost on said evaporatoris avoided.

3. In apparatus of the type described, in combination, a closed chamberincluding a wall structure formed of metallic plates secured togetherand having passages for the evaporation of refrigerant therebetween, anevaporator in said chamber, means for supplying refrigerant to saidevaporator and to said wall passages whereby said evaporator and thechamber wall structure are cooled, air propelling means in said chamberadjacent said evaporator and a flue closely enclosing said airpropelling means and said evaporator and having openings therein spacedfrom said cooled wall structure for directing air propelled by saidmeans successively at a high velocity over said evaporator and at alower velocity over said cooled wall structure, whereby frostaccumulations on said evaporator are removed.

4. In apparatus of the type described, in combination, a closed chamberincluding a wall structure formed of metallic plates secured togetherand having passages for the evaporation of refrigerant therebetween, anevaporator in said chamber, a window in said chamber spaced from saidevaporator, means for supplying refrigerant to said evaporator and tosaid wall passages whereby said evaporator and the chamber wallstructure ar cooled, and means including an air propellin device forcirculating air in said chamber successively at a high velocity oversaid evaporator and at a lower velocity over said cooled wall structureand said window, whereby frost accumulations are removed from saidevaporator and said window.

5. In apparatus of the type described, in combination, a closed chamberincluding a wall structure formed of metallic plates secured togetherand having passages for the evaporation of refrigerant therebetween,- anevaporator in said chamber, a window in said chamber spaced from saidevaporator, means for supplying refrigerant to said evaporator and tosaid wall passages whereby said evaporator and the chamber wallstructure are cooled, air propelling means in said chamber adjacent saidevaporator, and a flue closely enclosing said air propelling means andsaid evaporator and having openings therein spaced from said cooled wallstructure for directing air propelled by said means successively at ahigh velocity over said evaporator and at a lower velocity over saidcooled wall structure and said window, whereby frost accumulations onsaid evaporator and on said window are removed.

6. In apparatus of the type described, in combination, a closed chamberhaving an openable door therein, a window in said door, said chamberhaving a wall structure formed of spaced metallic plates securedtogether and providing passages therebetween for the evaporation ofrefrigerant, an evaporator in said chamber spaced from said door, meansfor supplying refrigerant to said evaporator and to said wall structurerefrigerant passages whereby said evaporator and the chamber wallstructure are cooled, air propell-i ng means adjacent said evaporator,and means for confining air propelled by said propelling means to a pathclosely adjacent said evaporator and for directing some of the air sopropelled in an unconfined circulatory path successively over saidcooled wall structur and said window, whereby air is circulated in saidchamber at a higher velocity over said evaporator and at a lowervelocity over said cooled wall structure and said window and frostaccumulations are removed from said evaporator and said window.

ERWIN LODWIG.

